Hey all, On my Hot Rod it has (1) Schroeder Steering Box and (2) Death Wobble. (1) Just wondering if someone knows how to adjust the box free play and how much free play should there be? (2) Death Wobble. I’ve read thru a lot of posts on this. My car would do it a lot till I put new tires on it, now it only happens at low speed if I hit a bump on left front. It feels and I can see the motor shaking badly. Only 2 ways to stop it 1) come to a complete stop or 2) accelerate thru it. It doesn’t happen if you’re at higher speeds and hit a bump. I seen a couple threads on “steering dampener” and caster. I will try to post pics of the front end. Any thoughts or suggestions will be greatly appreciated.
I run a steering dampener on all the straight axle cars I've had.. you need to try one... Your going to have a lot of people here tell u that cowl steering won't work...be prepared...lol
From what I can see from the picture you posted the angle of the drag link needs to be parallel to the angle of your Wishbone and it is way off. So you're going to have some pretty bad bump steer also.
Your pitman arm is adjustable, the first thing (it may require changing the headers) I would recommend is to drop the drag link so it is parallel with the wishbones/chassis When the draglink is running at an angle it can cause bump steer, and by dropping the draglink on the steering box end it will quicken the steering.
I built a 32 roadster 10-12 years ago with Schroeder steering (8to1) and had the drag link parallel with the hairpins and the ground, pitman arm center was slightly back of the ball end of the hairpins, everything in the front end was new and front alignment was right on. I had terrible death wobble. I called Ken (RIP) at the Rolling Bones and he said they use a steering stabilizer on all their builds. I installed one and the car drove perfect. One day when the Bones were at a stop in Nebraska on their way to Bonneville I had a chance to look at their Schroeder steered cars and they had steering stabilizers.
@BJR said it, and it's worth saying again. No no no no no! Nothing needs to be parallel to anything else. The bottom of the pitman arm needs to be as close as possible to the rear end of the wishbone, and no angle of anything enters into it. Why that is is explained repeatedly in the above-linked thread. I'll link it again, in case you've missed it: https://www.jalopyjournal.com/forum/threads/cowl-steering-just-stop.1101046/
Drag link parallel if using four bars, or in the exact same plane with same length and pivot point if wishbones. With your split wishbones, you are about one whole foot from proper geometry for the bump steer issues. All that said, the death wobble might actually be separate from bump steer. The death wobble might be caused by weak joints or flexy tube. Or caster improperly set. Or excessive scrub because the wheels are too offset. Or toe in not set proper.
Those are big front tires. What PSI are you running? Most folks air em up too much like they are driving a late model to 32 PSI which is wrong.
I would like to see the front attach point of the drag link. You might be able to cancel some of the bump steer by raising that point, ala Doane Spencer. The stabilizer is a must to deal with the wobble. Great looking car.
I come from a long line of oval track racers and chassis builders! Cowl steering and split bones were common in the the mid to late 60s in modified oval track racing. I have looked at that thread there is a bunch of bad information there, and when people started arguing with Dennis Frings one of the the top short track chassis builders in the country, it was pretty clear most who commented in that thread didn’t understand chassis or handling!
Check the caster....I run like 3 degrees positive and have never had a problem....When you run to much the wheels try to come back to center with to much force and then they try to return in a different direction...Like there trying to wrap around the kingpin...You see this a lot on drag cars that have a lot of caster for high speed stability....
Wish I wasn't such a dinosaur and could send pictures. I'd like to know what was wrong with the install and geometry on my deuce roadster. Everybody has an opinion.
To see exactly what happens to the geometry of your setup, jack up the front of the car, getting both tires off the ground. then put a 4 X 4 under the drivers side tire and let the front end down. Compare the draglink angles before and after. This will give you an idea of how much the draglink angle changes when you hit a bump. Proceed from there with modifications or the addition of a steering damper. Good luck
Interestingly enough. Before I headed out for a drive today I lowered the tire press. Front from 32 to 25, rear from 32 to 26. Was way worse, every little pebble. Drove back to the shop and aired up the front tires to 35. Much better, didn’t cure the slow speed wobble.
You may be getting a little bit of lateral movement with the early style tie rod ends? When I first built my 32 highboy pickup with 32/34 tie rod ends the NSRA inspector was a young kid who had never seen them before and he wouldn't pass me as he saw some movement in the tie rod ends because of them being spring loaded. His supervisor/dad explained that's the way they work and passed the truck. Many thousand miles later they're working just fine.
Your wheels could have more positive (inwards) offset to get the scrub radius a little better. And the way the panhard connects to the right hand bone could be tweaked. Otherwise, I can't see anything that is drastically out of place with the front end assembly. Read the thread that was recommended on cowl steering in posts #2 and #9. There is very good info in it. Some understand and some don't. Just follow the geometry, it doesn't lie......
One of your first questions was about free play in the steering gear. It should have very little. You can check it by removing the steering link at the pitman arm, hold the steering wheel stationary and try to move the arm back and forth. I'm guessing it should be in the 0.001 to 0.003 range. While I haven't worked on a Schroeder gear, I believe it is similar to a Halibrand gear. The Halibrand gear is a worm setup. If the Schroeder is the same, you adjust end play by loosening the case bolts and rotating the tubes the pitman shaft goes through. That will roll the driven gear into and out of mesh with the drive worm.
The rules of chassis, handling, and basic steering/suspension geometry are the same for street cars and racecars. Oval trackers have been using Schroeder type steering and split wishbones/hair pins radius rods long before the became the rage in hot rods. Still today midgets, sprinters, Silver Crown, and North East Sportsman and Modified stock cars use straight axles and Schroeder type steering. Do you really think modern oval track chassis builders or Kurtis Kraft builders of midgets, sprint cars, and Indy cars didn’t know or understand?
Have you tried it with the panhard off / disconnected ? It would seem to me that could be a chain reaction starter...
Just to be clear, death wobble and bump steer are two different issues. A solution to death wobble could be as easy as a steering damper, like a Fiero or VW Microbus. Limit caster to no more than seven degrees on a door car.
While I don't know anything about Sportsman or Modifieds, I do know that current dirt sprints use a 3-bar front end. Upper and lower on the right, lower only on the left, which is just a 4 bar with one bar left off to eliminate the natural binding of 4 bars in extreme articulation. Pavement sprints use a 4-bar front. Silver crowns use a 4-bar front. A 4-bar front end does require that the drag link be parallel with the 4 bars, making the Schroeder gear work for them, so all those chassis designers do know what they are doing.
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